If the input impedance in the pass band remains the same as the original then that suggests we should be able to add a 5.9K in series with the source voltage and that the output voltage will reduce by 50% without affecting the response.

I mounted breadboard the two options ("standard" and "modified") and measured input impedance in both circuits above 10 KHz. There may be slight discrepancies in the readings but I do not see major differences.

Ad post #75 and #77:
IMHO the blue curve seems to be more linear - standard differential amplifier seems to be the better circuit. The input impedance ist indeed 2.4k
Also with matched resistors the CMRR will be very good.

The blue curve is more linear than red (no doubt). However, in real cases, this nonlinearity does not exceed 0.1 dB. Believe me it is so.

The main intention in my connection is:Given a common connection, have the possibility to relocate its components, maintaining its current parameters and improve only the low-frequency response (without prejudice to the other parameters). This would allow us to implement it in all that exists, relocating connections only.

While what you have is very interesting, would have to find a way to keep the same input impedance (or something very similar).